Testing molten alumina



A ril 21, 1925.

534,032 L. W- GABRIEL I TESTING MOLTEN ALUMINA Filed Jan. 29. 1924 INVENTOR l. W flalire'el J I ATTORNEYJ Patented Apr. 21, 19 25.

LEO WILLIAM GABRIEL, 0F BADIN,

NORTH CAROLINA, ASSIGNOR TO ALUMINUM COMPANY .OF AMERICA, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

TESTING MOLTEN ALUMINA.

Application filed January 29, 1924. Serial N 0. 689,202.

To all whom it may concern:

Be it known that I, LEO W. GABRIEL, a citizen of the United States of America, residing at Badin, in the county of Stanly and State of North Carolina, have invented certain new and useful Improvements in Testing .Molten Alumina, of which the following is a full, clear, and exact description.

This invention relates to processes for obtaining alumina from bauxite or other aluminous materials by electrothermal reduc tion of associated non-aluminous oxids to elemental form and alloying the resulting elements together to permit separation thereof from the unreduced alumina. Thereduction is preferably carried out in an electric furnace, and when the operation is on a large scale, with the necessary high temperatures (around 2000 0.), difficulty is sometimes experienced in determining when the reactions have proceeded far enough, for tapping the furnace with the best results. If they have not gone far enough the alumina withdrawn contains too much of the unreduced impurities. On the other hand, if the reaction goes too far, an excessive amount of alumina is reduced. I have therefore been led to devise my present invention, which has for its chief object to provide a simple, convenient and trustworthy method of testing the furnace contents, particularly the unreduced alumina portion thereof, to determine whether the desired degree of purity of the latter has been attained.

The preferred way of testing the furnace contents by my method will be described in connection with its use in the reduction process disclosed in the copending application of William 'Hoopes, Francis C. Frary and Junius D. Edwards, Serial No. 608,283, filed December 21, 1922. For this process a furnace of the type illustrated herein may be used.

Referring to the accompanying drawing,

Fig. 1 shows the furnace, somewhat diagrammatically, in cross section;

Fig. 2, on a larger scale, shows the sampling or testing bar used to ascertain the quality of the molten alumina in the fur nace.

A'furnace of the type shown in Fig. 1, for treating about 25,000 pounds of material per day, may be about 15 feet long, 9 feet passed for cooling wide, and 7 feet high; with two cylindrical carbon electrodes, each about 6 feet in length and 18 inches in diameter, and each carrymg between 7,000 and 10,000 amperes of current, preferably alternating.

In the drawing, 10 designates an opentopped steel shell, containing a carbon bottom 11 and a refractory side lining 12 composed of fire brick, bauxite brick, or other suitable material. The carbon bottom slopes toward a tap hole 13 for withdrawing the alloy, and a tap hole 14 at a higher level permits withdrawal of the unreduced material (alumina) independently of the underlying metal. All these openings may be closed in any convenient manner. For example, a plug of pine wood may be driven into the hole, as indicated at 15. The heat encountered causes the plug to burst into flame immediately, and it is converted into charcoal in a few minutes, but it lasts long enough to stop the flow of slag and permit solidification at the back of theplug- The spent 16," preferably rather steep so as to prevent clogging by freezing due to rapid cooling of the slag or metal, may be lined with a mixture of magnesite and fire clay, moistened with a solution of water-glass.

Conducting members are embedded in the carbon bottom or lower electrode 11 for con nection with one terminal of a source of alternating current represented by the transformer 17. Preferably the conducting members are 'in the form of steel pipes, as indicated at 18, through which water may be purposes. The upper electrode consists of oneor more carbon cylinders, as 19, connected to the other terminal or terminals of the secondary of the transformer 17. If two electrodes are used they may be connected on the threewire system, with the furnace bottom 11 connected to the third wire. Any suitable means, not shown, maybe provided to raise and lower the electrodes and hold the same in position. The energy input can be regulated in any convenient way, for example by'varying the number of ampere turns in the transformer, preferably in the primary thereof, as indicated by the adjustable pr1- mary terminal 20.

Thefurnace shell may be cooled, 1f necessary or desirable, by water discharged upon the outer shell from an encircling plpe 21,

' arranged at the upper part of the shell and O in connected to a source of supply, not shown. The water running down the shell can be caught by a trough 22 and carried away by a drain pipe 23. To keep water out of the tap holes the latter may be provided with suitable shields, as 24. Y

When used for producing ferro-silicon and alu nina, the furnace builds up a linin as indicated at 25, for example, composed, especially in the lower part of the furnace, of charge and solidified slag.

For obtaining substantially pure alumina from bauxite (for example) the charge includes iron or other suitable metal, and a reducing agent. The latter is preferably in the form of coke; and the iron, which may be metallic or in the form of oxid, is for the purpose of taking up or absorbing iron, titanium and silicon reduced from oxids thereof present -in the bauxite. As the reaction goes on, the metals sink to the bottom and form a layer 26 of ferro-silicon alloy, while the unreduced alumina floats thereon as a layer of slag 27 Usually some alumina is also reduced and finds its way into the alloy, along with the other metals.

When it is judged that the reaction is complete or has gone far enough, I test the alumina layer to determine the condition thereof. This I do by thrusting an iron sampling rod or bar 28, Fig. 2, into the alumina and immediately withdrawing it. Allowing the adhering material to freeze in the air, I have found that the thickness,

and surface color and texture, of the layer of frozen alumina, shown (partly in section) at 29, afford a sufficiently accurate index of the conditions inside of the furnace. Thus I have observed that if the color is yellow (apparently the result of surface oxidation by the oxygen of the air), the tapped slag will contain about 1 per cent, or

more, of titanium oxid, and usually, though I an iron bar into the body of molten alumina, withdrawing the bar before fusionnot always, considerable iron oxid anc silica. On the other hand a gray or black surface indicates satisfactory elimination of titanium, and, generally, iron oxid and silica also, since the latter are more easily reduced than the former. Also, a thin smooth coating denotes a thin, fluid condition of the slag, which .would have little tendency to entrain the iron alloy when the slag is taped out, whereas a thick, rough coating indicates too low a temperature for satisfactory tapping.

When the coating has been inspected it is cracked off, to restore the rod to condition for re-use. I prefer an iron rod for the purpose, but any metal can be employed which will not be fused by its momentary immersion in the intensely hot alumina.

It is to be understood that the invention is not limited to the particular process herein described but can be used in other situations where it is desired to test molten alumina for the presence or absence of impurities of the kind mentioned.

I claim:

1. A method of testing a molten nonmetallic alumina-bearing product, comprising withdrawing a readily freezable sample thereof spread over a relatively large surface and permitting the same to solidify in the air, whereby characteristic color is produced on the surface exposed to the air.

2. A method of testing a molten nonmetallic alumina-bearing product obtained from raw material containing iron an titanium oxide and silica, comprising taking from such product while in the molten state a sample spread in a relatively thin layer, and allowing the same to solidify in the air, whereby the surface exposed to the air acquires a characteristic color.

3. A method of testing molton alumina for titanium, comprising thrusting a sampling bar momentarily into the molten alumina, withdrawing the bar with a relatively thin coating of alumina, and allowing the coating to solidify in the air, whereby the presence of titanium is evidenced by a yellow color on the surface exposed to the air, and the absence of titanium and more readily reducible oxids by a color ranging from gray to black.

l. A method of testing molton alumina in an electric furnace, comprising thrusting thereof, and allowing the alumina coating thereon to freeze in the air, whereby the surface exposed to the air acquires a color indicative of the purity of the alumina.

In testimony whereof I hereto afiix my signature.

LEO WILLIAM GABRIEL. 

